1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming system.
2. Description of Related Art
Conventionally, there have been known image forming systems in which sheet processing apparatuses for performing processing such as stapling are connected to image forming apparatuses such as MFPs (Multi Function Peripherals), copiers and printers.
Stapling is processing of accumulating a predetermined number of sheets of paper on which images are formed, and striking staples into the bundle of accumulated sheets to bind the sheet bundle to be a booklet. The stapled sheet bundle is ejected, by an ejection mechanism, to an ejection tray which is provided so as to protrude outside the sheet processing apparatus.
Here, operations of the ejection tray will be described with reference to FIG. 10A.
The ejection tray 201, as shown in FIG. 10A, includes a stacking surface 201a which is tilted upward from the base end portion to the distal end portion, and an abutting unit 202 to abut the rear end of the sheet bundle SS is provided near the base end portion of the stacking surface 201a. The ejected sheet bundle SS slides down the stacking surface 201a of the ejection tray 201 to abut the abutting unit 202 at the rear end, and thus is aligned to the sheet conveyance direction.
Further, when the sheet bundle SS is stacked on the stacking surface 201a, the ejection tray 201 is lowered for a predetermined distance and thus the fall distance of ejected sheet bundles SS is kept constant.
However, in a case of stacking sheet bundles SS on the ejection tray 201 as described above, as shown in FIG. 10B, there can be a phenomenon called rear end remaining that the rear end of the sheet bundle SS remains at a position of abutting the abutting unit 202 when the ejection tray 201 is lowered, and the sheet bundle may swell. This leads to a bad appearance and has caused, in some cases, stacking errors such as drop of the following sheet bundles which cannot be stacked stably.
Conventionally, there have been suggested various techniques as measures against rise and curling of the rear end portions of the sheets stacked on the ejection tray.
For example, Japanese Patent Application Laid Open Publication No. 2008-7207 describes a technique providing a scraping-off member which scrapes off the rear end of sheets immediately after the ejection and presses the rear end portions of the sheets ejected on the ejection tray to avoid the unnecessary rise.
In addition, Japanese Patent Application Laid Open Publication No. 2002-321861 describes a technique which includes a detection unit detecting that the uppermost position of the sheets stacked on the ejection tray reaches a predetermined position, and if the detection unit detects the sheet when the ejection tray stops, lowers the ejection tray until the detection unit does not detect the sheet.
However, the technique of Japanese Patent Application Laid Open Publication No. 2008-7207 does not simulate the above-mentioned rear end remaining which is caused by the lowering of the ejection tray, and is insufficient to completely solve the rear end remaining.
Also, the technique of Japanese Patent Application Laid Open Publication No. 2002-321861 merely lowers the ejection tray to a position where the sheet is not detected by the detection unit, and thus cannot solve the rear end remaining caused by the lowering of ejection tray.